Heavy duty commercial vehicles use a complex pneumatic air braking system. During the operation of the vehicle, brake actuators within the system convert pneumatic fluid pressure into braking torque to be selectively applied by the driver to service brakes and/or a continuous force to defeat the spring brakes, i.e. parking/emergency brakes.
FIG. 2 illustrates a known brake actuator having a service brake chamber 101a and a spring brake chamber 101b in a common housing. To employ the service brakes, increased pneumatic pressure is fed into actuator 100 causing diaphragm 103 to plunge push rod 102 which connects to an arm that turns the brake camshaft.
As brake linings wear, the stroke length of the push rod must be adjusted. This is accomplished by moving slack adjuster 110.
Typically, brake actuators also include provisions for engaging the spring brakes by means of power spring 104 caged in compression in chamber 101b of the housing. Continuous pneumatic pressure on diaphragm 105 during operation of the vehicle further compresses power spring 104 and disengages the spring brake allowing vehicle movement. When the pressure drops below a predetermined level, power spring 104 extends within chamber 101b to the predetermined limits and plunges push rod 102 to reengage the spring brake in turn hindering vehicle movement.
Known brake actuator housings comprise a canister typically formed as two or more clam shells 106, 107 connected together in a tamper-resistant manner by means of restraining or clamping devices 108, 109. Since the power spring has a high spring constant, its compressed state in the actuator imparts it with significant potential energy. The improvident removal of the restraining device of the power spring chamber releases the stored energy and turns the clam shell housing into a projectile.
Significant injury and even death has been known to occur from improper handling. Thus, numerous patents have issued that address restraining or clamping devices that seek to prevent tampering and improper handling. However, such devices only reduce the potential injury by hampering access to the power spring chamber. A determined or ill-advised mechanic or driver may still defeat this safety feature.
Other patents have issued that disclose rotary actuators returned to their pre-engaged position by torsionally loaded springs. However, each discloses covers that are conventionally secured and upon removal releases the stored energy turning the cover into a projectile.
Therefore, what is desired is a brake actuator that is safer yet is fully functional as a fluid operated brake actuator. What is also desired is a brake actuator that does not cage a power spring in compression. Further, what is desired is a brake actuator that reduces the number of components, is easy to manufacture, simple and cost effective to maintain, and/or readily installed on vehicles.